The present invention relates to a semiconductor device for use in sensor systems. More particularly, the present invention relates to a semiconductor device to be employed for compact and light sensor systems that are free of the need for battery replacement.
In recent years, people have come to be more mindful of requisites to good health; and, accordingly, they are seeing the need for various personal vital assistant instruments (hereinafter, to be described as “PVA” instruments) that facilitate the users in making it easier to perform health checks by themselves. The functions of these PVA instruments are similar to those of conventional expensive medical measuring instruments. However, unlike those expensive medical instruments, such PVA instruments need to be supplied at lower prices, so that the general public is able to purchase them. In addition, for patients of lifestyle-related illnesses, it is important for them to monitor their bodily temperatures and blood pressures continuously. To meet such requirements, PVA instruments also need to be simplified in configuration so that the users can measure their health conditions easily. More particularly, PVA instruments should be compact and light so that the users can carry them with them. To meet such requirements, PVA instruments that are housed in compact boards are now under development.
For example, such PVA instruments are disclosed in the official gazettes of JP-A No. 327472/2001 (hereinafter to be referred to as [document 1]) and JP-A No. 344352/2001 (hereinafter to be referred to as [document 2]). Each of the PVA instruments comprises a GSR (Galvanic Skin Reflex) electrode; a sensor board in which an acceleration sensor, a bodily temperature sensor, a blood pulse sensor, etc. are built; and a main board for communicating with the sensor board to collect sensor information through a Bluetooth low power wireless interface, for example, to analyze the physical condition, etc. of the user. In addition to the above-described sensors, the sensor board also includes a CPU, a memory, an A/D converter, a low power wireless interface, an amplifier, and a small battery. Furthermore, a dedicated board is provided for each of the sensors located on the sensor board. Information (analog values) received from each sensor located on the sensor board is amplified to a proper level, then converted to digital values in the A/D converter, and finally processed to information in a proper format by the CPU and transmitted to the main module through the low power wireless interface chip.
Among the above-mentioned sensors, the blood pulse sensor can detect changes in the state of the electrical impedance of the user's skin, as detected through a GSR electrode, whereby the user's mental condition or state (anger, etc.) can be determined. The blood pulse sensor can also measure the degree of saturation of the oxygen in the user's blood. In addition, the blood pulse sensor can also estimate the blood sugar level of the user and indicate the user's physical condition. Blood pulse intervals of the user make it possible to estimate the user's mental state to a certain degree. The blood pulse sensor is configured by a pair of elements, including an infrared/red LED and a semiconductor photo-diode. On the other hand, the acceleration sensor is configured by acceleration sensors of three axial directions, and it is used to estimate the posture, motion, or the like of the user. The user can thus know the diagnostic result transmitted to his/her wrist watch, headset, portable telephone, or similar device through its built-in low power wireless interface.
On the other hand, an RFID chip, which is configured by a simple RF circuit, a low performance CPU, and a low capacity memory (non-volatile memory or the like), that are integrated in a semiconductor integrated circuit having a size which is a few millimeters square and under, is disclosed in Nikkei Electronics (Feb. 25, 2002, pp. 112–137 (hereinafter to be referred to as [document 3]). The RFID chip disclosed in the document 3 has its specific ID written in its built-in non-volatile memory and the ID is read through an RF reader, so that the RFID chip is used as an identification tag for a product, just like a barcode. More specifically, such an ID is read through a RFID reader by detecting the Q value of an LC oscillation circuit that is configured by a coil and a capacitor to be changed by a high frequency irradiated on the RFID chip. This detection is carried out in a non-contact manner.
In addition to such an ID, product information or the like also can be written in the non-volatile memory of the RFID chip. For example, as disclosed in the official gazette of JP-A No. 187611/2001 (hereinafter to be described as [document 4]), such an RFID chip is applied to a food (ex., beer barrels, etc.) distribution management system. In the system disclosed in document 4, an RFID chip, a sensor board, and an ID tag provided with a sensor configured by a small battery are embedded in each beer barrel and the temperature of the beer barrel read by the sensor is written and stored as needed in the non-volatile memory located in the RFID chip. And, when the beer barrel is delivered to the user, the user reads the temperature information, stored during the delivery, through use of an RF reader. Such a configuration of the RFID chip makes it possible for the user to know whether or not the temperature of the beer barrel has been controlled properly during the transportation through the electronically recorded information read from the chip.
On the other hand, the official gazette of JP-A No. 58648/2002 (hereinafter to be referred to as [document 5]) discloses an example of the use of an RFID chip for locating positions. In this example, an RFID chip is attached to each of a plurality of animals, such as mice used for experiments. In this connection, a mouse cage is divided into small square areas and a plurality of RFID readers are arranged so that one RFID reader is disposed in each of the square areas. Then, information read by each of the plurality of RFID readers is registered continuously to detect the movement of a target mouse. The ID information of each RFID chip can also be used more effectively to distinguish among mice individually. In this case, the configuration of the RFID chip makes it possible to determine how each mouse is moving in the cage individually.
There have also been some attempts in which such semiconductor microchips are embedded in a user's body, so that the user can obtain auxiliary helpful information from the microchips. For example, the official gazette of JP-A No. 293128/5 (hereinafter to be referred to as [document 6]) discloses a technique in which microchips are embedded in the vocal organ of a user, so that vibration of the vocal cords is detected and transmitted through an RF circuit to an external pseudo voice generation apparatus, so as to artificially produce vocal sounds, instead of by means of the user's vocal cords. More specifically, the chips are embedded in a plurality of positions, such as the pharynx, the larynx, the respiratory tract, the face, the mouth, the nasal cavity, etc. so that the vibration sensor in each chip detects the vibration at each of these positions, thereby to enable the pseudo voice generation apparatus to analyze the vocal sounds the user wants to utter. This will become a great help for the user whose vocal cords have been damaged.
The IEEE Computer July 2000 (pp. 42–48 (hereinafter to be described as [document 7]) also recognizes an effect in which floors, walls, human bodies, etc. are always vibrating slightly, so that each of those items usually has an energy density of about mW/cm3.
On the other hand, a configuration of a power collection circuit is disclosed in the IEEE TRANSACTIONS ON VERY LARGE SCALE INTEGRATION SYSTEMS, VOL. 9, NO. 1, February 2001 (pp. 64–75) (hereinafter to be referred to as [document 8])).
A high frequency switch formed in the MEMS process is disclosed in EDN Japan, 2002, No. 5 (pp. 55–61) (hereinafter to be referred to as [document 9]).
A UWB (Ultra Wide Band) radio communication method is disclosed in Nikkei Electronics, Mar. 11, 2002 (pp. 55–66) (hereinafter to be referred to as [document 10]). According to the technique described in this document 10, a correlator is needed for receiving data in the UWB. The correlator correlates pulse strings supplied from a receiver pulse generator with received pulse strings.
A power generator that generates electric power through electromagnetic inductance is disclosed in IEEE Proc. Circuits Devices Syst., Vol. 148, No. 6 December 2001 (hereinafter to be referred to as [document 11]).
The PVA instrument disclosed in each of the documents 1 and 2 uses a general CPU and a sensor board. The PVA instrument thus makes it easier for the user to perform his/her health management without using any expensive medical instrument. Such a PVA instrument, however, needs a battery for both the sensor board and the main board, respectively. The instrument thus comes to become very heavy (up to a few hundreds of grams). Because a plurality of semiconductor circuits and other circuits are assembled on a board, it is unavoidable that the instrument will increase in size to a certain extent (up to the card size). Consequently, the burden on the user increases, particularly when the user uses the PVA instrument for a long time. In addition, because the PVA instrument is powered by a battery, the user is required to periodically replace the battery. And, while each sensor is connected to the main board wirelessly through a low power wireless interface, each sensor is also connected to the sensor board through an ordinary wire, so that the PVA instrument comes to face some minor difficulties and problems in both operation and durability.
On the other hand, the RFID chip disclosed in the document 3 does not need any battery, and it is compact in size. Thus, it can be attached to various objects, such as small animals, like mice, human beings, food products, etc. However, as described in connection with the conventional techniques, because the Q value of the LC resonant circuit is controlled to transmit signals to each RFID reader, the size of the external inductor L is determined by the subject RF signal wavelength (=1/frequency). And, because it does not have its own power source, it is operated only when RF signals are applied to the RFID chip from each RFID reader. This is why the RFID chip is considered to be not suitable for detecting information from the user's living body (bodily temperature, blood pulse, etc.) over a long period of time, since such a long time detection is indispensable for the PVA instruments.
The RFID tag to be attached on each beer barrel disclosed in the document 4 is provided with a small battery so as to keep it working for a long time. As a result, the RFID chip size is limited only in the card size, so that the feature of the RFID chip that “a compact and light-weight tag can be stuck at any place” is sacrificed.
In the document 5, such an RFID chip is used to detect the movement of each mouse. In this connection, the RFID reader disposed in each of the square areas is required to keep transmitting RF signals. The power of the RF signal transmitted from each RFID reader is about a few hundreds of milliwatts, so that the total power becomes a considerably large value. This makes it difficult to realize low power consumption in the RFID chip.
In the document 6, semiconductor microchips are embedded in a human body so as to realize a pseudo voice generating device. To embed semiconductor microchips in the human body in such a way, surgery is needed. The user's physical and mental burdens will thus increase significantly. However, the document 6 discloses no concrete configuration for the embedded semiconductor chips, nor does it disclose how to power the chips when no battery is embedded together with those chips, although this is a very important item.